Looking to use barrel hinges for some boxes making .Wood is all 1/2 inch thick . Don’t know where to start . Believe wood needs to be cut at a 45 degree angle for top and back piece to match up . Any and all help is welcome thanks guys

The top and back will need to be beveled at 45 degrees in my experience. You want to drill the holes before you bevel the edges. Plus you will want to make sure you have the depth correct for the holes and spaced evenly from side to side and front to back. Can be tricky to line up for assembly.